The present disclosure relates to a machine tool, in particular a grinding machine, comprising a workpiece mount, a tool unit, a measuring device and comprising a control device which is connectable to the measuring device and the tool unit. The present disclosure also relates to a method for measuring a workpiece, in particular a workpiece diameter, in a machine tool, in particular a grinding machine.
Machine tools, in particular grinding machines, are known in the prior art. Thus, for example, cylindrical grinding machines can comprise rotationally symmetrical tools, for instance grinding wheels, which can interact in a suitable manner with a workpiece for removing material. Cylindrical grinding machines can be configured, for example, for external cylindrical grinding, internal cylindrical grinding or plunge-cut grinding or angular plunge-cut grinding. As well as grinding wheels, abrasive belts can also be used in principle for cylindrical grinding. As well as rotationally symmetrical faces, eccentrically shaped workpiece faces, for instance, can also be machined when the workpiece mount and the tool unit are drivable in a suitable manner and movable in relation to one another. For instance, camshafts, crankshafts or similar workpieces with eccentric geometries can be machined or ground in this way.
A workpiece to be machined can be accommodated, for instance, between two centers of a workpiece mount or, however, on one side in a workpiece mount. Also known is so-called centerless grinding where the workpiece is not accommodated between centers in the grinding machine, but can be accommodated and guided, for instance, by means of bearing rails, regulating wheels, guide rollers or the like.
DE 10 2009 042 252 A1 discloses a grinding machine which has a measuring apparatus which is configured for in-process measuring of test items during a machining operation. For this purpose the measuring apparatus has a measuring head which is connected to a basic body of the measuring apparatus so as to be pivotable by means of a linkage. The measuring head has an extendible measuring probe which is coupled to a measuring prism and is provided to determine the diameter or the roundness of the test item. The linkage is configured for being able to complete movements of the test item over a certain region, for example a rotation of a crankshaft journal of a crankshaft about the rotational axis thereof.
In-process measuring can be effected, in this way in principle even in the case of grinding eccentrically arranged cylindrical faces, at least section by section. This can be effected at the same time as the grinding. However, the measuring apparatus has a complex design. The linkage is developed in a costly manner and is expensive to control in operation.
So-called in-process measuring, that is, measuring during a machining operation, can allow for highly precise machining operations and can contribute to increasing the quality of manufacture and the process reliability. For this purpose, however, it is regularly necessary to provide for each workpiece measurement to be measured, that is, for instance for each diameter, a measuring head which is matched precisely to the expected measurement. This can be a single-purpose measuring head, for instance, or however, a measuring head on which, for instance, two measuring probes are adjustably accommodated which are at a spacing from one another which corresponds to the expected spacing. The measuring probes are each to be adapted and correspondingly aligned in a highly precise manner to the measurement to be tested.
Such an in-process measuring head is shown, for instance, in DE 196 16 353 A1. Expensive setting-up, adjusting or calibrating processes, which are necessary in order to adapt the measuring head for the respective purpose, can be disadvantageous in this case. In particular in the case of single unit machining, with small batches and medium batches, the setting-up of the measuring head can result in not insignificant expenditure of time and money.
Against this background, it must already be stated that the measuring apparatus known from DE 10 2009 042 252 A1 is sometimes not able to meet the measuring accuracies necessary for an in-process measurement. The associated measuring head has a measuring probe and a measuring prism which are coupled to an absolute measurement reference by means of a plurality of linkage elements of the linkage. All deviations along the path of individual elements of the kinematic chain of the linkage can influence the position of the measuring head in relation to the test item. This can be disadvantageous in particular in the case of section by section measuring of eccentric workpieces. The position of the measuring head in relation to the test item, for instance in relation to the angular position thereof, can contain errors.